1. Field of the Invention
The present invention relates to a positioning control method for positioning a workpiece and a tool of a machine tool. The positioning control method has a rapid traverse command for moving the tool and/or the workpiece to a predetermined position at a maximum speed and a linear interpolation command for moving the tool and/or the workpiece while conducting linear interpolation. The present invention also relates to a numerical control apparatus for conducting the positioning control method, a numerical control program-generating apparatus for enabling the positioning control method and a computer-readable recording medium for recording a program for conducting the positioning control method.
2. Description of Related Art
Conventionally, a rapid traverse command is input to a numerical control apparatus (referred to "NC apparatus" hereinafter) to determine a relative position of a workpiece and a tool in a processing method of the workpiece by controlling a machine tool by the NC apparatus. The rapid traverse command relatively moves either the workpiece or the tool at a maximum speed, and thus, rapidly positions the workpiece and the tool for accelerating processing work. In Japan, a basic command code of the NC apparatus is defined in JIS-B-6314. The rapid traverse command is defined to be a sequence of command following a "G00" code.
In positioning control, a final relative position of the workpiece and the tool is of greater importance than the method of reaching the position. Accordingly, when the rapid traverse command is inputted to the NC apparatus adding a target position of the tool, the tool is accelerated gradually to move at the maximum speed and is decelerated as it approaches the target position, as shown in acceleration-deceleration process P1 of FIG. 6.
If a command of "G00X100Y200" (move the tool to X=100 mm and Y=200 mm at a rapid traverse) is sent in a multi-axis positioning control, the X-axis, Y-axis and Z-axis position are independently controlled. And an in-position check which compares the target position and the tool's actual position is conducted after completing the position shift.
However, the positioning control by the rapid traverse command includes an acceleration-deceleration process from a standstill to the maximum speed or a reverse thereto. Accordingly, when the tool moves short as shown in P2 of FIG. 6, the tool and the like enters the deceleration process before reaching the maximum speed, and the workpiece is not positioned by sufficient high-speed.
Furthermore, the in-position check is conducted after stopping the tool according to the positioning control of the rapid traverse command as described above. Accordingly, extra time for the check is necessary, requiring longer time when the movement distance is short, so that the workpiece is not positioned by sufficient high-speed.
As described above, the movement speed of the tool and the like does not reach the maximum and in-position check is necessary at every stop point when a sequence of the rapid traverse command is employed for moving the tool and the like at a relatively short distance. Accordingly, there is a limit in speeding up an entire processing of the workpiece including the positioning control of the tool and the like.